As is known, in managed pressure applications, there is a need to dynamically and effectively control fluid pressure within a wellbore during drilling. More specifically, it is important to maintain drilling fluid in a wellbore at a pressure less than or equal to the fluid pressure of a geological formation in order to prevent drilling related problems such as stuck pipes, loss of circulation and excessive use of drilling mud.
Drilling fluid is required during drilling operations to lubricate the drill bit and carry drill cuttings to the surface. Typically, drilling fluid is pumped downwardly through the drill pipe to the drill bit whereupon it returns upwardly to the surface through the wellbore annulus. Drilling fluid returning to the surface will be affected by gravity and friction encountered along the walls of the wellbore thereby increasing the hydrostatic pressure at the bottom of the wellbore.
Managed Pressure Drilling (MPD) is an adaptive drilling process used to precisely control the annular pressure profile throughout a wellbore. More specifically, MPD allows bottom hole pressure adjustments with minimal interruptions to the drilling process. The annular pressure profile is controlled such that it is balanced or nearly balanced. The objective of MPD is to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly.
MPD uses a closed, pressurizable fluid system to control the annular pressure profile. More specifically, the annular pressure in the wellbore is controlled through adjustments in backpressure, fluid density, fluid rheology, annular fluid level, circulating geometry, hole geometry or the like.
Similarly, Underbalanced Drilling (UBD) uses a closed and pressurizable fluid system wherein the annular wellbore pressure profile is less than the fluid pressure in the formation being drilled. Annular pressure in the wellbore is similarly controlled through adjustments in backpressure, fluid density, fluid rheology, annular fluid level, circulating geometry, hole geometry and the like.
In order to prevent drilling related problems as described above, MPD and UBD decrease the Equivalent Circulating Density (ECD) by lowering the hydrostatic pressure of drilling fluid. A low density drilling fluid can mitigate the risk of a well becoming overbalanced and developing drilling problems. A gas is often injected into a drilling fluid in order to reduce the drilling fluid density. Some gases commonly used for drilling fluid injection include air, nitrogen, natural gas and processed flue gas. As is known, the use of natural gas and/or processed flue gas may increase the combustible and/or corrosive nature of the drilling fluid.
Furthermore, in MPD and UBD, drilling fluid is naturally heated while traveling to and from the drill bit by the drilling process and/or geological formations. As a result, drilling fluid often reaches temperatures greater than 65 degrees Celsius (149 degrees Fahrenheit) and can exceed 85 degrees Celsius (185 degrees Fahrenheit). Furthermore, drilling fluid may be comprised of or accumulate combustible and corrosive components during the drilling process.
As in other drilling operations, managed pressure and underbalanced drilling require a Blowout Preventer (BOP) to prevent an uncontrolled release of formation fluids from the wellbore. A release may cause significant damage to a drilling rig and injuries or fatalities to rig personnel. As a result, MPD and UBD further require that a Rotating Control Device (RCD) be installed on the top of the BOP stack to form a positive pressure seal on the drill pipe and safely divert drilling fluid away from the drill floor. An RCD typically contains a radial insert that forms a seal around the drill pipe.
As is known, RCD inserts are generally radial and fabricated from synthetic rubber such as neoprene or nitrile rubber. During drilling, the drill pipe is axially forced downwards through the RCD and RCD insert such that over time the RCD insert will incur wear and tear as the insert slidably engages the drill pipe. Thus, as a result of normal use, RCD inserts will deteriorate and become less effective over time. Furthermore, in particular, high temperature drilling fluid and/or any corrosive components of a drilling fluid will accelerate the deterioration of an RCD insert.
An RCD insert manufacturer will typically recommend a maximum operating lifetime before which RCD inserts should be replaced to ensure safe and productive operation of a drilling rig. The replacement of an RCD insert requires considerable Non Productive Time (NPT) as the drill string must be broken and the RCD disassembled. Accordingly, there continues to be a need for systems that can increase the time between RCD insert replacements.
As noted, temperature and/or corrosive drilling fluid may cause accelerated deterioration of an RCD insert such that the accelerated deterioration of an RCD insert may cause the premature and/or unexpected failure of the insert before the expiration of the manufacturer recommended maximum operating lifetime. Any premature or unexpected failure can present a significant safety risk to personnel if drilling fluid is released onto the drill floor.
Thus, while RCD inserts are currently manufactured to resist the corrosive chemical properties or high temperatures of returned drilling fluid, RCD inserts are generally not designed to resist the combination of both the corrosive chemical properties and high temperatures of returned drilling fluids found in many drilling operations.
More specifically, as is known to one of skill in the art, RCD inserts are generally designed to perform specifically to a recommended maximum operating temperature (typically 65-85° C.). Increases in temperature and/or corrosive drilling fluid compositions can decrease the operating lifetime of an RCD insert. Thus, the maximum operating lifetime of an RCD insert can be extended (and the risk of premature failure reduced) by decreasing the temperature of returned drilling fluid at the RCD insert/drilling fluid interface and/or moderating the composition of returned drilling fluid coming into contact with the RCD insert.
It is therefore an object of the present invention to improve the useful life of an RCD insert by providing a system and method for lowering the temperature and moderating the composition of returned drilling fluid coming into contact with an RCD insert within an RCD.
A review of the prior art reveals that a number of technologies have been used in the past for cooling inserts in a Rotating Control Device. For example US Patent Publications 2006/0144622 and 2008/0210471 to Bailey et al. disclose Rotating Control Devices (RCDs) having thermal transfer systems for circulating cooling fluid inside radial RCD seals.
U.S. Pat. Nos. 6,749,172 and 7,004,444 to Kinder disclose Rotating Control Devices (RCDs) having two independent fluid circuits for cooling and lubrication between a rotating body and the RCD casing.
Other references include U.S. Pat. No. 5,662,181 which describes circulating chilled water or antifreeze through the top seal packing box of an RCD and U.S. Pat. No. 5,277,249 which describes an RCD having a heat exchanger and fluid circuits for cooling radial seals in a packer assembly.
While the prior art may provide a partial solution, each are limited in various ways as briefly described below.
In particular, past systems may be limited as they do not suggest or teach the advantages of a cooling system in which the cooling fluid is in direct contact with the hot drilling fluid. More specifically, previous systems do not suggest a system to prevent hot drilling fluid from directly contacting the radial RCD inserts. Furthermore, previous systems do not teach moderating the composition of drilling fluid across the interface of a radial RCD insert.